Unknown,Transcriptomics,Genomics,Proteomics

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The Mi-2 homolog, Mit1, actively positions nucleosomes within heterochromatic domains to suppress transcription

ABSTRACT: Nucleosome positioning is both active and passive and regulates access to the genome for replication, transcription and repair. Here we report that Mit1, a subunit of the fission yeast SHREC complex similar to Mi-2/NuRD, regulates transcription at regions of heterochromatin by positioning nucleosomes to preclude access to RNA Polymerase II. Purified Mit1 is a nucleosome remodeling factor capable of mobilizing histone octamers on short DNA fragments and requires ATP hydrolysis and chromatin tethering domains to remodel nucleosomes and silence transcription. We propose that SHREC is recruited to heterochromatin to mobilize nucleosomes onto unfavorable positions to prevent spurious transcription within heterochromatin. M-bM-^@M-^C RNA samples were prepared from biological duplicates of WT and mit1M-bM-^HM-^F::NatMX6 fission yeast to compare transcript levels using the Affymetrix GeneChip S.pombe Tiling 1.0FR microarray.

ORGANISM(S): Schizosaccharomyces pombe

SUBMITTER: Geoffrey Neale

PROVIDER: E-GEOD-46649 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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The Mi-2 homolog Mit1 actively positions nucleosomes within heterochromatin to suppress transcription.

Creamer Kevin M KM Job Godwin G Shanker Sreenath S Neale Geoffrey A GA Lin Yuan-chi YC Bartholomew Blaine B Partridge Janet F JF

Molecular and cellular biology 20140324 11

Mit1 is the putative chromatin remodeling subunit of the fission yeast Snf2/histone deacetylase (HDAC) repressor complex (SHREC) and is known to repress transcription at regions of heterochromatin. However, how Mit1 modifies chromatin to silence transcription is largely unknown. Here we report that Mit1 mobilizes histone octamers in vitro and requires ATP hydrolysis and conserved chromatin tethering domains, including a previously unrecognized chromodomain, to remodel nucleosomes and silence tra ...[more]

PMID: 24662054

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Project description:Maintenance of the correct level and organization of nucleosomes is crucial for genome function. Here we uncover a role for a conserved bromodomain AAA-ATPase, Abo1, in maintenance of nucleosome architecture in fission yeast. Cells lacking abo1+ experience both a reduction and mis-positioning of nucleosomes at transcribed sequences in addition to increased intragenic transcription, phenotypes that are hallmarks of defective chromatin re-establishment behind RNA polymerase II. Abo1 is recruited to gene sequences and associates with histone H3 and the histone chaperone FACT. Furthermore, the distribution of Abo1 on chromatin is disturbed by impaired FACT function. The role of Abo1 extends to some promoters and also to silent heterochromatin. Abo1 is recruited to pericentromeric heterochromatin independently of the HP1 ortholog, Swi6, where it enforces proper nucleosome occupancy. Consequently, loss of Abo1 alleviates silencing and causes elevated chromosome mis-segregation. We suggest that Abo1 provides a histone chaperone function that maintains nucleosome architecture genome-wide. A chromatin-seq/MNase-seq approach called Chromatin Particle Spectrum Analysis (Kent et al., (2011) Nucleic Acids Res. 39:e26) was used to map and compare nucleosome position in wild-type (strain 972) and isogenic abo1 knock-out (strain HM463) fission yeast cells. For each strain, three independent in vivo MNase digest bio-reps were performed and the purified DNA pooled. CPSA was performed using paired-end mode Illumina technology with pooled samples multiplexed over two HiSeq2000 lanes. Each CPSA paired read describes a microcococcal nuclease (MNase) resistant DNA species from chromatin, with the insert-size equivalent to the size of DNA protection. For each strain type, two analysed data sets are provided here: one listing the genomic distribution of MNase-protected DNAs of 150bp (â150bp CPSA size classâ) and corresponding to mono-nucleosomes; the other listing the genomic distribution of MNase-protected DNAs of 300bp (â300bp CPSA size classâ) and corresponding to di-nucleosomes.

Project description:Abstract: In the yeast S. pombe, multiple chromatin-modifying enzymes are required for heterochromatin formation, yet how their actions alter chromatin structure to block access to DNAby the transcriptional machinery is unknown. We constructed high-resolution nucleosome occupancy maps of heterochromatic regions in wild-type strains and in mutants lacking the H3K9 methyltransferase Clr4 or one of the two activities of the silencing effector complex SHREC. Fourier analysis reveals that these enzymes do not increase the regularity of nucleosome spacing. Rather, their principal effect was to induce the elimination of nucleosome-free regions (NFRs). Both NFRs associated with transcription initiation sites as well as those not associated with promoters are affected. As in S. cerevisiae, repressed genes in euchromatin retain their NFRs. Thus, NFR elimination cannot be explained as a secondary consequence of repression. The maps also show that TFIIIC boundary elements have NFRs resistant to silencing, suggesting a potential role in preventing lateral spread of heterochromatin. NFR elimination offers a mechanism by which heterochromatin restricts access of the transcriptional machinery to DNA. Nucleosome positions in either heterochromatin or euchromatin were mapped in various mutants to determine whether chromatin structure is altered upon heterochromatic silencing. Eight strains were assayed for nucleosome positioning in heterochromatin while two strains were assayed for nucleosome positioning in euchromatin. Two biological replicates were assayed for each strain. No dye swaps were done. RNA transcripts were also mapped using the heterochromatin tiling arrays to determine where RNA transcripts accumulate in heterochromatin. Three strains were assayed for transcripts in heterochromatin by hybridizing cy5-labeled cDNA created from total RNA against cy3-labeled cDNA created from RNA synthesized from sonicated genomic DNA. Two biological replicates were assayed for each strain.

Dataset Information

The Mi-2 homolog, Mit1, actively positions nucleosomes within heterochromatic domains to suppress transcription

Publications

The Mi-2 homolog Mit1 actively positions nucleosomes within heterochromatin to suppress transcription.

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